Generation of vortices and observation of Quantum Turbulence in an oscillating Bose-Einstein Condensate

We report on the experimental observation of vortex formation and production of tangled vortex distribution in an atomic BEC of Rb-87 atoms submitted to an external oscillatory perturbation. The oscillatory perturbations start by exciting quadrupolar and scissors modes of the condensate. Then regular vortices are observed finally evolving to a vortex tangle configuration. The vortex tangle is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud has suppression of the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion.Comment: to appear in JLTP - QFS 200

The anomaly of the oxygen bond-bending mode at 320 cm−1^{-1} and the additional absorption peak in the c-axis infrared conductivity of underdoped YBa2_{2}Cu3_{3}O7−δ_{7-\delta} single crystals revisited by ellipsometricmeasurements

We have performed ellipsometric measurements of the far-infrared c-axis dielectric response of underdoped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ single crystals. Here we report a detailed analysis of the temperature-dependent renormalization of the oxygen bending phonon mode at 320 cm$^{-1}$ and the formation of the additional absorption peak around 400-500 cm$^{-1}$. For a strongly underdoped YBa$_{2}$Cu$_{3}$O$_{6.5}$ crystal with T$_{c}$=52 K we find that, in agreement with previous reports based on conventional reflection measurements, the gradual onset of both features occurs well above T$_{c}$ at T*$\sim$150 K. Contrary to some of these reports, however, our data establish that the phonon anomaly and the formation of the additional peak exhibit very pronounced and steep changes right at T$_{c}$. For a less underdoped YBa$_{2}$Cu$_{3}$O$_{6.75}$ crystal with T$_{c}$=80 K, the onset temperature of the phonon anomaly almost coincides with T$_{c}$. Also in contrast to some previous reports, we find for both crystals that a sizeable fraction of the spectral weight of the additional absorption peak cannot be accounted for by the spectral-weight loss of the phonon modes but instead arises from a redistribution of the electronic continuum. Our ellipsometric data are consistent with a model where the bilayer cuprate compounds are treated as a superlattice of intra- and inter-bilayer Josephson-junctions

Self-similar expansion of the density profile in a turbulent Bose-Einstein condensate

In a recent study we demonstrated the emergence of turbulence in a trapped Bose-Einstein condensate of Rb-87 atoms. An intriguing observation in such a system is the behavior of the turbulent cloud during free expansion.The aspect ratio of the cloud size does not change in the way one would expect for an ordinary non-rotating (vortex-free) condensate. Here we show that the anomalous expansion can be understood, at least qualitatively, in terms of the presence of vorticity distributed throughout the cloud, effectively counteracting the usual reversal of the aspect ratio seen in free time-of-flight expansion of non-rotating condensates.Comment: 8 pages, 4 figure

Vortices and dynamics in trapped Bose-Einstein condensates

I review the basic physics of ultracold dilute trapped atomic gases, with emphasis on Bose-Einstein condensation and quantized vortices. The hydrodynamic form of the Gross-Pitaevskii equation (a nonlinear Schr{\"o}dinger equation) illuminates the role of the density and the quantum-mechanical phase. One unique feature of these experimental systems is the opportunity to study the dynamics of vortices in real time, in contrast to typical experiments on superfluid $^4$He. I discuss three specific examples (precession of single vortices, motion of vortex dipoles, and Tkachenko oscillations of a vortex array). Other unusual features include the study of quantum turbulence and the behavior for rapid rotation, when the vortices form dense regular arrays. Ultimately, the system is predicted to make a quantum phase transition to various highly correlated many-body states (analogous to bosonic quantum Hall states) that are not superfluid and do not have condensate wave functions. At present, this transition remains elusive. Conceivably, laser-induced synthetic vector potentials can serve to reach this intriguing phase transition.Comment: Accepted for publication in Journal of Low Temperature Physics, conference proceedings: Symposia on Superfluids under Rotation (Lammi, Finland, April 2010

Tree method for quantum vortex dynamics

We present a numerical method to compute the evolution of vortex filaments in superfluid helium. The method is based on a tree algorithm which considerably speeds up the calculation of Biot-Savart integrals. We show that the computational cost scales as Nlog{(N) rather than N squared, where $N$ is the number of discretization points. We test the method and its properties for a variety of vortex configurations, ranging from simple vortex rings to a counterflow vortex tangle, and compare results against the Local Induction Approximation and the exact Biot-Savart law.Comment: 12 pages, 10 figure

From Coherent Modes to Turbulence and Granulation of Trapped Gases

The process of exciting the gas of trapped bosons from an equilibrium initial state to strongly nonequilibrium states is described as a procedure of symmetry restoration caused by external perturbations. Initially, the trapped gas is cooled down to such low temperatures, when practically all atoms are in Bose-Einstein condensed state, which implies the broken global gauge symmetry. Excitations are realized either by imposing external alternating fields, modulating the trapping potential and shaking the cloud of trapped atoms, or it can be done by varying atomic interactions by means of Feshbach resonance techniques. Gradually increasing the amount of energy pumped into the system, which is realized either by strengthening the modulation amplitude or by increasing the excitation time, produces a series of nonequilibrium states, with the growing fraction of atoms for which the gauge symmetry is restored. In this way, the initial equilibrium system, with the broken gauge symmetry and all atoms condensed, can be excited to the state, where all atoms are in the normal state, with completely restored gauge symmetry. In this process, the system, starting from the regular superfluid state, passes through the states of vortex superfluid, turbulent superfluid, heterophase granular fluid, to the state of normal chaotic fluid in turbulent regime. Both theoretical and experimental studies are presented.Comment: Latex file, 25 pages, 4 figure

Youth representations of environmental protest

A necessary condition for a functioning democracy is the participation of its citizens, including its youth. This is particularly true for political participation in environmental decisions because these decisions can have intergenerational consequences. In this article we examine young people’s beliefs about one form of political participation - protest - in the context of communities affected by fracking and associated anti-fracking protest, and discuss the implications of these representations for education. Drawing on focus groups with 121 young people (age 15-19) in 5 schools and colleges near sites which have experienced anti-fracking protest in England and Northern Ireland, we find young people well-informed about avenues for formal and non-formal political participation against a background of disillusionment with formal political processes and varying levels of support for protest. We find representations of protest as disruptive, divisive, extreme, less desirable than other forms of participation, and ineffective in bringing about change but effective in awareness-raising. These representations are challenging, not least because the way protest is interpreted is critical to the way people think and act in the world. These representations of environmental protest must be challenged through formal education in order to safeguard the UN Convention on the Rights of the Child and ensure that the spirit of Article 11 of the UK Human Rights Act is protected

Geographic Expression Of Aids Epidemic In Campinas, Southeastern Brazil, Between 1980 And 2005

Objective: To analyze the spatial distribution of reported AIDS cases in adults and its association with living conditions in the city of Campinas, Southeastern Brazil. Methods: Data on AIDS cases in men (n=2,945) and women (n=1,230) aged more than 13 years and living in Campinas, recorded in the SINAN (Brazilian Information System for Notifiable Diseases), were used to map the spatial distribution of this disease and the male:female ratio. Maps were constructed for the following periods: from 1980 to 1995, from 1996 to 2000, and from 2001 to 2005. The variables included in the analysis were address, sex and age. A weighted composite index was used to study living and health conditions in the area. Patients' home addresses were geocoded on a cartographic base, after correction and standardization according to a reference database of streets. A generalized additive model was adjusted to analyze the spatial distribution of the ratio of male:female cases in space, in the three study periods. Results: The ratio of male:female cases was higher in areas with better living conditions (central) and around the prison (northwestern), where families of prisoners and former prisoners live temporarily, while this ratio was lower in the city suburbs (southwestern). Conclusions: The trends towards the AIDS epidemic affecting more women and poorer individuals were confirmed by the decrease in the ratio of male:female cases in the period, particularly in vulnerable and impoverished populations. Geographic information systems and spatial data analysis can be useful for AIDS control and surveillance actions.445812819Bailey, T., Spatial Statistics Methods in Health (2001) Cad Saude Publica, 17 (5), pp. 1083-1098. , DOI:10.1590/S0102-311X2001000500011Barcellos, C., Acosta, L.M.W., Lisboa, E.P., Brito, M.R.V., Flores, R., Estimativa da prevalência de HIV em gestantes por análise espacial, Porto Alegre (2006) RS. Rev Saude Publica., 40 (5), pp. 928-930. , DOI:10.1590/S0034-89102006005000007Carvalho, M.S., Souza-Santos, R., Análise de dados espaciais em saúde pública: métodos, problemas, perspectivas (2005) Cad Saude Publica, 21 (2), pp. 361-378. , DOI:10.1590/S0102-311X2005000200003Castilho, E.A., Chequer, P., Struchiner, C., A epidemiologia da AIDS no Brasil (1994) A Aids no Brasil (1982-(1992), pp. 59-67. , Parker R, Bastos C, Galvão J, Pedrosa JS, organizadores. Rio de Janeiro: Relume-DumaráDias, P.R.T.P., Nobre, F.F., Análise dos padrões de difusão espacial dos casos de AIDS por estados brasileiros (2001) Cad Saude Publica, 17 (5), pp. 1173-1187. , DOI:10.1590/S0102-311X2001000500018Fonseca, M.G.R., Bastos, F.I., Derriço, M., Andrade, C.L.T., Travassos, C., Szwarcwald, C.L., Aids e grau de escolaridade no Brasil: evolução temporal de 1986 a (1996) (2000) Cad Saude Publica, 16 (SUPPL 1), pp. 77-87. , DOI:10.1590/S0102-311X2000000700007Fonseca, M.G.R., Bastos, F.I., Vinte e cinco anos da epidemia de HIV e Aids no Brasil: principais achados epidemiológicos (2007) Cad Saude Publica, 23 (SUPPL 3). , DOI:10.1590/S0102-311X2007001500002Kelsall, J.E., Diggle, P.J., Spatial variation in risk of disease: a nonparametric binary regression approach (1998) Apl Stat, 47, pp. 559-573. , DOI:10.1111/1467-9876.00128Krishnan, S., Dunbar, M.S., Minnis, A.M., Medlin, C.A., Gerdts, C.E., Padian, N.S., Poverty, gender inequalities and women's risk of Human Immunodeficiency Virus/AIDS (2008) Ann N Y Acad Sci, 1136, pp. 101-110. , DOI:10.1196/annals.1425.013Quinn, T.C., Overbaugh, J., HIV/AIDS in women: an expanding epidemic (2005) Science, 308 (5728), pp. 1582-1583. , DOI:10.1126/science.1112489Rezende, E.L.L.F., Pascon, A.R.P., Pereira, G.F.M., Givisiez, J.M., Sousa, A.I.A., Arruda, M.R., Sakita, K., Cunha, A.R.C., Cenario Epidemiologico (2009) Bol Epidemiol Aids DST, 6 (1), pp. 43-50Santos, N.J.S., Tayra, A., Silva, S.R., Buchalla, C.M., Laurenti, R., A Aids no Estado de São Paulo. As mudanças no perfil da epidemia e perspectivas da vigilância epidemiológica (2002) Rev Bras Epidemiol, 5 (3), pp. 286-310. , DOI:10.1590/S1415-790X2002000300007Takahashi, R.F., Shima, H., de Souza, M., Mulher e Aids: perfil de uma população infectada e reflexões sobre suas implicações sociais (1998) Rev Latino-Am Enferm, 6 (5), pp. 59-65. , DOI:10.1590/S0104-11691998000500008Tomazelli, J., Czeresnia, D., Barcellos, C., Distribuição dos casos de AIDS em mulheres no Rio de Janeiro, de 1982 a 1997: uma análise espacial (2003) Cad Saude Publica, 19 (4), pp. 1049-1061. , DOI:10.1590/S0102-311X2003000400027Wallace, R., Wallace, D.U.S., Apartheid and spread of AIDS to the suburbs: a multy-city analysis of the political economy of spatial epidemic threshold (1995) Soc Sci Med, 41 (3), pp. 333-345. , DOI:10.1016/0277-9536(94)00349-